1. Technical Field
The invention relates generally to semiconductor fabrication, and more particularly, to methods for fabricating a back end of the line (BEOL) interconnect structure with liner and seed materials for integration of conductive materials on the substrate layer of the semiconductor.
2. Background Art
The current trend of diminishing critical dimensions of semiconductor devices presents fill issues with the conventional fabrication methods of interconnect layers using a seed layer of conductive wiring material. Noble metals as liner layers have been adopted in light of thermodynamic stability, good adhesion, and immiscibility with conductive wiring materials where fill issues are eliminated. The fairly low electrical resistivity of noble metals, like ruthenium (Ru), enables direct electroplating of conductive wiring materials, like copper (Cu), making this an essential and advantageous feature due to better electrical performance and a wider process window for later Cu plating.
With these advantages, noble metals are good alternative liner materials in place of conductive wiring materials as seed layers. As illustrated in FIG. 1, however, it is a challenge to remove a noble metal liner layer 14 using conventional chemical-mechanical polishing (CMP) such that the noble metal layer 14, first liner layer 12, hard mask 10 and conductive wiring material 20 are coplanar. The polishing removal rate of noble metals, like ruthenium (Ru) is comparatively lower than that of conventional liner materials like tantalum nitride (TaN), tantalum (Ta), titanium (Ti), titanium (TiN). Hardware and the chemistries for existing CMP process need to be modified due to this difference. Such modification is costly and disruptive to the semiconductor fabrication process. Introduction of a new material may also require development or use of new slurries in the CMP process as compared to existing slurries used in the removal of barrier materials like tantalum nitride (TaN) and titanium nitride (TiN).
In view of the foregoing, there is a need in the art for a solution to the problems of the related art.